APPENDIX C: SHARING CRITERIA FOR THE 1670-1675 MHZ BAND

INTRODUCTION

As discussed elsewhere in this report, the 1670-1675 MHz band will become available for mixed use in
1999 subject to the continued operation of meteorological satellite (METSAT) downlinks. NTIA has
decided to permit immediate mixed use on a more restricted basis: all Government operations must be
protected until the spectrum transfer in 1999. These operations include METSAT downlinks received
at Wallops Island, Virginia and Fairbanks, Alaska, and radiosonde transmissions received at a large
number of locations throughout the United States and its possessions (US&P). The National Weather
Service (NWS) provided the following sharing criteria for compatibility with radiosondes and ground
receivers in the 1670-1675 MHz band.

PROTECTION FOR RADIOSONDES

The largest user of radiosondes within the US&P is NWS, which considers the following sharing criteria
adequate to protect its operations. The reader should be aware that radiosondes are also operated by
a number of other Federal organizations, such as DOD, DOE, NASA, and NSF. These operations are
at times and places unrelated to NWS, and their protection criteria may differ. Accordingly, it will be
necessary for non-Federal users of the band also to coordinate with these agencies prior to licensing. In
addition, radiosondes are operated by various non-Federal entities, such as universities and state and
local governments.

For compatibility with NWS, the power density in the 1670-1675 MHz range from all sources and from
all azimuths at each NWS ground-based receiver site must not exceed the following limits:

Power density in a 1.3 MHz bandwidth shall not exceed [-150 dBW/(meter)^2] more than 0.24%
of the time, nor [-135 dBW/(meter)^2] more than 0.03% of the time. These power densities
correspond to field strengths of 0.67 microvolts/meter and 3.5 microvolts/meter respectively.
These levels are applicable during the hours of 2300-0200 Universal Time (UT) and 1100-1400
UT every day. During periods of abnormal weather and special research programs, protection
must be provided at additional times. These special events can last 3 or more hours and may
cover one or more launch sites. During current or anticipated regional level severe weather
conditions when the accuracy of weather forecasts, warnings or alerts could affect safety-of-life
and property for communities, means must be provided by the non-Federal user(s) to shut down
their transmitters within 10 minutes of being notified and prior to radiosonde release.
The non-Federal transmitters shall remain off until the end of the radiosonde
flight(s). NOAA agencies such as the National Severe Storms Laboratory and the
Hurricane Research Division require these specialized radiosonde
flights for severe weather and hurricane forecasting.

PROTECTION FOR METSAT RECEIVERS

Wallops Island, Virginia, is the location of the Command and Data Acquisition (CDA) station used to
control NOAA's Geostationary (GOES) satellites. For GOES-7, the currently operational spacecraft,
the receiver thermal noise level is -145 dBW into a 20 MHz bandwidth centered on 1681.6 MHz.

In the new generation of GOES satellites, called GOES I through M, the received signal will occupy the
band centered on 1676 MHz with a 5.0 MHz bandwidth. The noise level is not currently known. The
first of these satellites, the former GOES-I, now called GOES-8, is currently in its operational
demonstration phase. Should tests be completed successfully, it will replace Meteosat-3 around
February, 1995. GOES-7 will eventually be replaced by GOES-9 around early 1996. In an emergency
(e.g., failure of an operational satellite), GOES-7 may be recalled to operational status at any time up
to the end of its useful life, estimated to be about two years.

The criterion for adequate protection of the CDA stations at Wallops Island and Fairbanks is as follows:

The cumulative interference at the receiver input in any 1 kHz band can be no higher than
10 dB below the receiver thermal noise power in that band, for 99.99 percent of the time
during any one-month period.

The cumulative interference at the receiver input in any 1-Hz band can be no higher than
the receiver thermal noise power in that band, for 99.99 percent of the time during any one
month period.

For purposes of coordination, the receiver noise temperature in the band 1670-1675 MHz is assumed
to be 50 Kelvins. Therefore the thermal noise power at the receiver input is -182 dBW in 1 kHz, and
-212 dBW in 1 Hz. The receive antenna gain is assumed to be 49 dBi, and the antenna is pointed at the
geosynchronous arc between 75 W and 135 W longitude.

Appendix 28 of the ITU Radio Regulations is customarily used to develop coordination contours for
satellite stations. However, this Appendix contains no coordination criteria for METSAT ground
stations -- they are currently under development -- and makes certain assumptions regarding the
number and characteristics of the terrestrial stations with which the satellite ground stations must share
the band. In the present case, there is no way to predict the use of the band by non-Federal users. It will
therefore be necessary to coordinate all proposed ground systems, regardless of type or location.
Moreover, the use of airborne or satellite transmitters in this band must be avoided.